1. Field of the Invention
The present invention generally relates to a direct injection internal combustion engine and more particularly relates to such an engine in which the fuel is supplied in a stratified manner with a lean mixture proximate a spark plug electrode and a rich mixture proximate a cylinder wall.
2. Description of the Related Art
Japanese Patent Application No JP-A-2000-345944 disclosed a direct injected internal combustion engine. The engine comprised a cylinder bore and a cylinder head. A piston was positioned in the cylinder bore and reciprocated therein. The cylinder head had an intake passage in one side portion and an exhaust passage in the other side portion. A fuel injection valve was provided that injected fuel obliquely downward from one side of the cylinder head into the cylinder bore. A spark plug was located approximately on a central longitudinal axis of the cylinder bore. The spark plug had an electrode, or discharging part, that was positioned within the cylinder bore. The electrode would ignite the air-fuel mixture contained within a combustion chamber portion of the cylinder bore.
During operation, the fuel injection valve injected fuel during a compression stroke of the piston. The injected fuel collided with a top surface of the piston. The collision directed the injected fuel toward the electrode of the spark plug as shown in FIGS. 7 and 8 in the patent document. In other words, a rich air-fuel mixture layer was positioned about the electrode, which would reliability ignite during operation of the internal combustion engine. A more lean air-fuel mixture layer would adjoin the rich air-fuel mixture and the more lean mixture would be ignited by the flame generated when the rich air-fuel mixture ignited. This is known as a stratified charge combustion method. As used herein stoichiometric is an air-fuel mixture of 14.7:1 and a leaner mixture has a higher than stoichiometric ratio (e.g., 17:1) while a richer mixture has a lower than stoichiometric ratio (e.g., 12:1).
When stratified charge combustion is established, ignition can be reliably achieved as described above and greater fuel efficiency can be achieved. The improved fuel efficiency results because a portion of the overall air-fuel mixture contains less fuel relative to the region proximate the electrode. Reliable combustion of the overall lean mixture results even during low load operation.